Nonwoven fabrics and methods of manufacturing the same



June 11, 1963 A. H. DRELICH NONWOVEN FABRICS AND METHODS OFMANUFACTURING THE SAME 3 Sheets-Sheet 1 Filed Dec. 30, 1959 r M W & w ww M M a z w A m M m M T T M 1%. m a M N MM 2 A M 4,0. @M Z a m fi x {M 04 Z m m ml M M 1 1 e T w 2 w M N z A. k w 5 J June 11, 1963 A. H.DRELICH 3,093,502

NONWOVEN FABRICS AND METHODS OF MANUFACTURING THE SAME Filed Dec. 30,1959 5 Sheets-Sheet 2 90 aZwe/JYZ 90 aw Tlqltl.

June 11, 1963 A. H. DRELICH 3,093,502

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United States Patent 3,093,502 NONWOVEN FABRICS AND METHODS OFMANUFACTURING THE SAME Arthur H. Drelich, Plainfield, N.J., assignor, bymesne assignments, to Johnson & Johnson, New Brunswick, N J., acorporation of New Jersey Filed Dec. 30, 1959, Ser. No. 862,923 12Claims. (Cl. 117-38) The present invention relates to nonwoven textilefabrics and to methods of manufacture thereof, and particularly tofibrous webs bonded with cellulosic binders, which binders have beenreacted with a formaldehyde crosslinking compound.

The invention is of primary importance in connection with nonwovenfabrics composed of cellulosic fibers, no matter how produced; i.e.,carded, air-laid, water-laid, and the like. One such nonwoven fabric isexemplified by a product disclosed in the Goldman Patent 2,039,312 andsold under the trademark Masslinn. Another nonwoven fabric suitable foruse in this invention is a rayon and cotton web impregnated withcellulose regenerated from viscose and sold under the trademark Viskon.

Some of the so-called Masslinn nonwoven fabrics composed of textilefibers, the major proportion of which are oriented predominantly in onedirection, are described in greater particularity in US. Patent2,880,111 issued March 31, 19-59, to Arthur Drelich et al.

Other nonwoven fabrics disposed at random and not predominately orientedin any one direction, are described in U.S. Patents 2,676,363 and2,676,364 issued April 27, 1954, to C. H. Plummer et al. Other nonwovenfabrics are composed of fibers which were originally predominantlyoriented in one direction but which have been reorganized and rearrangedin predetermined designs and patterns of openings and fiber bundles,such as fabrics made by the process disclosed in U.S. Patent 2,862,251.

Illustrative cellulosic binders are: cellulose regenerated from viscose,cuprammonium solutions, and the like, cellulose derivatives such as thealkyl ethers and esters of cellulose and other water-sensitive celluloseanalogs such as chitin.

It has been discovered that the wet strength and wet abrasion resistanceof a cellulose bonded fabric may be increased by reacting it with aformaldehyde cross-linking compound. The concentration of thecross-linking compound in the impregnating solution must be very low inorder that the treatment only or substantially only effects the bondswithout undue degradation. The choice of catalyst and its concentrationare also important in execution of the cross-linking. Cellulose bondedfabric treated in the manner disclosed herein has excellentlaund'erability and wet abrasion resistance.

Elementary formaldehyde or compounds which decompose to liberateformaldehyde, or resins, usually nitrogeneous, which containformaldehyde in reactive form, may be employed in the practice of thisinvention. Particularly preferred for this purpose are water-solubleprecondensates or low polymers of methylolurea, methylolmelamine and thelike.

Many substances are known to catalyze the reaction of formaldehyde andcellulose. These are in general acidic substances, such as the commonmineral acids, or substances which become acidic at the elevatedtemperatures at which the reaction takes place; e.g., tartaric acid,lactic acid, boric acid, various sulfonic acids, oxalic acid, aceticacid, formic acid, salts such as ammonium thiocyanate, ammonium acidphosphate, ammonium chloride and the like.

Although the inventive concept will be described in particular withreference to a specific cellulose binder, for

Patented June 11, 1963 example cellulose xanthate, such is merely forillustrative purposes and is not be construed as limitative of thebroader aspects involved.

As is well known in the art, cellulose xanthate is readily prepared byreacting carbon bisulfide with suitably aged alkali cellulose anddissolving the reaction product in dilute sodium hydroxide solution. Theamount of regenerated cellulose, or cellulosic material added to thefabric may vary widely with the fabrics treated and the effects desired,but will usually be within the limits of a few tenths percent to 10 to15 percent by weight or higher. After application of the cellulosexanthate, the cellulose is regenerated and by-products and excessreagents are removed by washing. This fabric may be dried by exposure totemperatures of approximately 250 F. prior to the formaldehydeimpregnation. However, in certain instances it will be desirable toimpregnate the bonded web with a cross-linking compound prior to drying.In the impregnation steps the liquid pick-up may vary widely but usuallywill be between the limits of somewhat less than percent up to 200percent or higher.

The concentration of the formaldehyde in the finished fabric will liewithin the range of from about 0.l% to about 0.8% by weight, dependingon the structure and composition of the fabric, the finish desired, andother considerations. The preferred concentration of the formaldehyde inthe finished fabric is from about 0.15% to about 0.6%. At formaldehydecontents below the lower limit, the protective action is insuificientfor practical benefit. Upper limits of the range are set by thedevelopment of undesirable effects on the fabric. As the formaldehydecontent is raised, the fabric first begins to lose water absorbency asthe fibers themselves pick up the cross-linking agent. hyde content, thebinder becomes brittle, and the fabric as a whole is damaged to thepoint of uselessness. The

final formaldehyde content in the fabric is analyzed by a colorimetricmeasuring method based on the reaction of chromotropic acid withformaldehyde in concentrated sulphuric acid, as is well known in theart.

'In the formaldehyde impregnation step, the catalyst concentration isalso important. concentrations should be used; but the concentrationlimits depend on the acid strength of the catalyst material. Theconcentration of the catalyst should not be more than the amount whichlowers the pH of the cured fabric about 0.5 units. It is preferred thatthe catalyst concentration does not lower the fabric pH a significant ormeasurable amount. One of the catalysts for formaldehyde cross-linkingis sulfuric acid, and when this is used in accordance with thepresentinvention, the optimum catalyst concentration is about 0.05 percent (N/assuming 100% liquid pickup of the resin solution. At this solutionpickup the range for the sulfuric acid catalyst is from about 0.025percent to about 0.1 percent (N/20-0 to N/S'O). This Normality range ishigher than that desired when using a-very strong acid catalyst such ashydrochloric; but lower than can be used for weak acids or acid salts,or materials which decompose on heating with acid reaction, such asmagnesium chloride, ammonium thiocyanate, lactic acid, and the like.Concentrations of 0.5% by weight may be used when such catalysts areemployed in accordance with this invention. When using a higherconcentration of catalyst than that specified, the fabric is tenderedand loses its strength; while if a smaller amount of the catalyst thanthat specified above is used, excessive amounts of unbound formaldehydeare present, which is inefiicient and wasteful, and the freeformaldehyde contaminates the air around the curing apparatus.

At further increases in formalde-' Generally low-catalyst,

The cross-linking agent may be cured at conditions previously known inthe art, such as exposure for two minutes in air at 350 F. However, inaccordance with the present invention, cure conditions do not need to beas stringent as these prior art conditions; e.g., the crosslinking agentmay be cured by exposure to temperatures on a heated can of about 310 F.for as little as about one-half minute or as much as about five minutes.

Instead of solutions or dispersions of cellulose xanthate, othersolutions or dispersions fromwhich cellulose can be regenerated orprecipitated so as to become a permanent or substantially permanent partof the fabric, may be employed in the practice of the invention, forexample, cellulose in cuprammonium solution, or in certain quaternarysolvents. In addition there are certain cellulose compounds, dispersiblein and precipitatable as such from aqueous, or alkaline aqueous media,which can be sirniliarly employed, e.g., cellulose ethers and esters ofa suitable degree of substitution, such as the methyl, ethyl or propylethers and esters, and carboxymethyl and hydroxyethyl ethers ofcellulose, and the like. The terms dispersion and dispersed as used inthe present specification and claims are intended to include all of theforegoing, whether they be true solutions or colloidal dispersions.Those cellulosic materials generally applied in the arts in solution inorganic solvents are unsuited for the purpose of the invention. Asexemplary of this class of materials, nitrocellulose may be cited.

In describing the invention reference will be made to the accompanyingdrawings setting forth preferred embodiments thereof.

FIGURE 1 is an enlarged plan view of a portion of a nonwoven fabricbonded with Wavy or sinuous continuous lines of binder agent extendingsubstantially transversely across the nonwoven fabric and generally atright angles to the longitudinal axis thereof;

FIGURE 2 is an enlarged plan view of a portion of a nonwoven fabricbonded with discontinuous lines of binder agent extending substantiallytransversely across the nonwoven fabric and at right angles to thelongitudinal axis thereof;

FIGURE 3 is an enlarged plan view of a portion of a nonwoven fabricbonded with continuous lines of binder agent extending angularly acrossthe nonwoven fabric;

FIGURE 4 is an enlarged plan view of a portion of a nonwoven fabricbonded with discontinuous lines of binder agent extending angularlyacross the nonwoven fabric;

FIGURE 5 an enlarged plan view of a portion of a nonwoven fabric bondedin a square pattern of intersecting parallel rows of circular binderareas;

FIGURE 6 is an enlarged plan view of a portion of a nonwoven fabricbonded in a diamond pattern of intersecting parallel rows of circularbinder areas;

FIGURE 7 is an enlarged plan view of a portion of a nonwoven fabricbonded in a square pattern of intersecting parallel rows of squarebinder areas;

FIGURE 8 is an enlarged cross-sectional view of the portion of thenonwoven fabric illustrated in FIGURE 7, taken on the line S8 thereof;

FIGURE 9 is an enlarged front cross-sectional view of a portion of anonwoven fabric made by a prior act method;

FIGURE 10 is an enlarged side cross-sectional view of the nonwovenfabric illustrated in FIGURE 9;

FIGURE 1 1 is an enlarged plan view of a portion of a continuouslybonded nonwoven fabric.

In the preferred embodiments of the present inventive concept shown inthe drawings, a portion of a carded, nonwoven textile fabric 10 isillustrated in FIGURE 1 wherein sinuous binder segments 12 extendgenerally transversely across the width of the nonwoven fabric 10. Inthis configuration, the wavy binder segments 12 (when considered ingross) are substantially at right angles to the so-calledmachine-direction or the long axis of the nonwoven fabric 10. It is tobe appreciated, however, that if an isotropic nonwoven fibrous web madeby air deposition or other techniques is employed, or if anynon-oriented fibrous nonwoven fabric is used, the binder segments 12 mayextend longitudinally of the length of the fabric, or in its so-calledmachinedirection. The unbonded portions 14 which extend between thebinder segments 12 are sharply marked and clearly defined. Such a binderpattern is suitable for oriented, non-oriented, or rearranged nonwoventextile fabrics. The binder segments 12 are diffused substantiallycompletely through the nonwoven textile fabric 10 directly in straightlines from one surface of the fabric to the other surface, in the formof relatively soft and flexible, individually distinct open networks ofbonded fibers. FIGURE 8 illustrates the directness and sharpness of thediffusion.

In FIGURE 2, a portion of a carded, nonwoven fabric 20 is illustratedwherein the binder segments 22 are discontinuous and appear asrectangular areas on the surface of the fabric 20. The bidder segments22 are spaced apart by gaps of unbonded portions 24. Again, it is to berealized that the discontinuous binder segments 22 may, if desired,extend along the long axis of the nonwoven fabric, rather than acrossthe same, particularly in the case of non-oriented fibrous nonwovenfabrics. Such binder patterns are suitable for oriented, non-oriented,or rearranged nonwoven fabrics. Geometrically speaking, the bindersegments 22 are substantially right rectangular prisms having arectangular base and a rectangular upper surface, as shown in FIGURE 2,and substantially rectangular lateral faces which extend perpendicularlyto the surfaces of the nonwoven fabric 20.

In FIGURE 3, a portion of a carded, nonwoven fabric 30 is illustratedwherein the binder agent is in the form of substantially straight,continuous binder segments 32, separated by unbonded portions 34,extending angularly across the Width of the fibrous nonwoven fabric. Asshown, the binder segments 32 and the unbonded portions 34 are at anangle of about 75 to the long axis of the web. If desired, this anglemay, of course, be decreased to as low as about 0", particularly fornon-oriented nonwoven fabrics. Such a binder pattern is suitable fororiented, non-oriented, or rearranged nonwoven fabrics.

In FIGURE 4, a portion of a carded, nonwoven fabric 40 is illustratedwherein the binder segments 42 are discontinuous, extending angularlyacross the width of the fibrous nonwoven fabric. Unbonded portions 44lie between and separate the discontinuous binder segments 42. As shown,the binder segments are at an angle of about 7 to the long axis of theweb. If desired, this angle may be decreased to a low as about 0,particularly in the case of non-oriented nonwoven fabrics. Such a binderpattern is suitable for oriented, nonoriented, or rearranged nonwovenfabrics. Geometrically speaking, the binder segments 42 are right prismsand may appear on the surface of the nonwoven fabric either asparallelograms or rectangles.

In FIGURE 5, a portion of a random-laid nonwoven fabric 50 isillustrated wherein the binder segments 52 form a square pattern ofintersecting parallel rows of circular binder segments which areseparated by an unbonded portion 54. The diameters of the circularbinder segments are, of course, equivalent in width and spacing to thelines of binder segments previously described. That is, the diameters ofthe circular binders range from about 0.006 inch to about 0.050 inch andpreferably from about 0.010 inch to about 0.040 inch, with from about 8to about 30 binder segments per inch, and preferably from about 10 toabout 24 binder areas per inch, as measured in the long direction of thenonwoven web. The inter-circular spaces 56 in the lines of binder areasare of the same order as previously described, namely, from about 0.006inch to about 0.050 inch, and preferably from about 0.020 inch to about0.040 inch. The inter-circular spaces 56 are preferably equal but arenot necessarily so. Such a binder pattern is preferred for non-orientednonwoven fabrics.

In FIGURE -6, a portion of a random-laid nonwoven fabric 60 isillustrated wherein the binder agent forms a diamond pattern ofintersecting parallel rows of circular binder areas of segments 62, thediameter and the number of bonds per inch of nonwoven fabric as measuredin the direction of the long axis of the web as well as theinter-circular distance 66, being within the ranges described inconnection with the circular binder pattern of FIGURE 5. Such a binderpattern is prefered for non-oriented nonwoven fabrics.

In FIGURES 5 and 6 which are plan views, the binder areas or segments52, 62 have been illustrated and described as circular. In reality, thebinders are actually in the form of substantially right circularcylindrical networks of bonded fibers. The binder is didusedsubstantially uniformly throughout the binder segment and is notconcentrated solely on the surface of the nonwoven fabric. As a result,the binder segments 52 and 62 are neither dense nor solid masses but arerelatively soft and flexible and do not create a pebbly or nubby feel.

In FIGURE 7, a portion of a random-laid nonwoven fabric 70 isillustrated wherein the binder agent forms a square pattern ofintersecting parallel rows of square binder segments 72 separated by anunbonded portion 74. The sides of the squares have lengths of from about0.006 inch to about 0.050 inch and preferably from about 0.010 inch toabout 0.040 inch. The number of binder areas per inch of nonwoven fabricmeasured along the long axis thereof ranges from about 8 to about 30 andpreferably from about 10 to about 24. The intersquare distance 76between the segments of binder may rang-e from about 0.006 inch to about0.050 inch and preferably from about 0.020 inch to about 0.040 inch.Such a binder pattern is preferred for non-oriented nonwoven fabrics.

In FIGURE 7 which is a plan view, the binder segments 72 have beenillustrated and described as squares. In reality, the binders areactually in the form of substantially right square prism networks ofbonded fibers, the cross-sections of the networks being substantiallysquare from base to top surface. The binder is diffused substantiallyuniformly throughout the binder segment and is not concentrated solelyon the surface of the nonwoven fabric. As a result, the binder segments72 are relatively soft and flexible and do not create a pebbly or nubbyfeel.

In FIGURE 8, there is illustrated a cross-section of the portion of thenonwoven fabric 70 illustrated in FIGURE 7. It is to be observed thatthe binder segments 72 are substantially rectangular in cross-sectionand that they extend substantially completely through the nonwovenfabric from one surface to the other surface. In some cases, slightconcavities have been observed in the upper and lower surfaces of thebinder segments but these are relatively small and have no undesirableelfect on the properties and characteristics of the nonwoven fabric.

' The proportion of the weight of the binder material in the bindersegments to the weight of the fibrous ma terial in these binder segmentsis an important factor in determining the softness, drape and hand ofthe finishednonwoven fabric and of particular criticality with regard tothe pebb'ly, nubby or pirnply feeling. This proportion may be computedby a precise chemical analysis or more quickly with less accuracy bydetermining the amount of binder add-on in the binder segments from theweight of the nonwoven fabric before and after bonding. The weight ofthe fibrous materials in .these binder areas is the fractional coverageof the binder multiplied by the weight of the dry nonwoven web. In theforegoing embodiments of the invention, the percent coverage is fromabout 10% to about 50%, and preferably from about 12% to about 35% ofthe dry nonwoven web.

The nonwoven fabrics which may be used in accord ance with thisinvention may be bonded by any of the known methods of bonding such asimpregnation, spraybonding and applying the binder in spaced areas ofthe web by rotogravure techniques, employing a preliminary step ofwetting the fibrous web with from about 70% to about 250% by weight ofan aqueous liquid, based on the weight of the dry web. The surfacecoverage of the fibrous web by the binder may range from about 1% toabout 100%, but it is preferred that the surface coverage be at leastabout 10%. The amount of binder add-on based on the weight of thefibrous web should be from about 0.3% to about 15%.

The finished fabrics of this invention will range from about 100 grainsper square yard to about 2,000 grains per square yard, though it ispreferred that the weight of the finished fabric be from about 175grains per square yard to about 1,000 grains per square yard.

In FIGURES 9 and 10, there are illustrated cross-sections at rightangles to each other of a portion of a nonwoven fabric which is anotherembodiment of the invention. This nonwoven fabric has binder lines orareas 82 (FIGURE 9) which extend in one direction on the upper surfaceof the nonwoven fabric 80 and are separated by unbonded areas 84. Otherbinder lines or areas 86 (FIGURE 10) are disposed on the lower surfaceof the nonwoven fabric 80 and extend in a direction normal to thedirection of binder lines 22. These latter binder lines 86 are separatedby unbonded areas 88. It will be apparent from FIGURES 9 and 10 that thebinder lines 82 and 86 have not diffused or penetrated uniformly orcompletely through the non-woven fabric 80 and that they merely lie inparallel lines in each surface of the fabric to form intersectingover-all parallel grid patterns. These patterns meet each other at theintersections 90 which are located approximately in the center of thenonwoven fabrics. The surfaces of the bonds 82 and 86 are hard and flatand create a nubby and pebbly feeling. Slight concavities are formed inthe. faces of the bonds 82and 86 and impart a corrugated effect.

In FIGURE 11 which is an enlarged plan view, the binder 102 is diffusedsubstantially uniformly throughout the nonwoven fabric 100, and tends tocoat the fibers 104.

In order to facilitate-a clear understanding of the invention, thefollowing preferred specific embodiments are described in detail.

Example 1 A dry all-rayon nonwoven fabric weighing 750' grains persquare yard containing about 7% regenerated cellulose deposited in afine-line pattern to function as a binder (as described below) isimpregnated in a mangle with a solution containing 1% of an essentiallymonomeric methylolmelarnine cross-linking agent (sold by AmericanCyanamid Company as Aerotex UM), and N/ sulfuric acid. Solution pickupfrom the bath is about 100% based on the weight of the air dry nonwovenfabric. The fabric is rapidly dried in a tenter frame at 260 and curedin an oven by exposure to 350 F. temperature for two minutes; The boundformaldehyde content of the fabric is found by analysis to be 0.34%,occurring principally in the binder cellulose as determined by means ofchemical staining tests.

After completion of the curing operation, the fabric is 7 used as awet-wiping cloth for dishes, counters, tabletops,

walls, and for heavy duty usein washing automobiles.- The treated andcured fabric shows a 5-fold increase in service life as compared to ananalogous fabric which does not have the cross-linking treatment.

In a comparative test, the methylolmelamine monomer is applied from a 5%solution. Catalyst concentration is '4 maintained at N/ 100 H 50 Boundformaldehyde content as determined by analysis is 1.7%. The fabric haspoor absorbency and is very stiff and is not a desirable washcloth.

Example 2 The procedure of Example I is followed, except that thecross-linking agent is methylolurea (sold by Rohm & Haas as Rhonite313), and the bound formaldehyde content is found by analysis to be0.16%; and a fabric similar to that described in Example 1 is obtained.

In a comparative test, this example is repeated except that thecross-linking agent is methylolurea applied from 4% solution with N/ 25H 50 as catalyst. The bound formaldehyde content is found by analysis tobe 0.55%. After curing, the nonwoven fabric is badly tendered andunsuitable for use.

This example demonstrates the deleterious effect of raising the amountof acid catalyst used in the impregnation step. It should be noted that,in accordance with the present invention, the concentration of acidcatalyst must be kept within the limits previously prescribed ratherthan maintaining a constant ratio of acid catalyst to formaldehyde as isoften done in normal practice,

Example 3 The procedure of Example 1 is repeated, except that thecross-linking agent is a substituted methylol triazone (sold by DanRiver under the trade name Stanset Z-98) and its bound formaldehydecontent is found to be 0.29%; and similar results are obtained.

Example 4 The procedure of Example 1 is followed, except that the basefabric to which the cross-linking agent is applied contains 100% cottonfiber; and similar results are obtained.

Example 5 The procedure of Example 1 is repeated, except that the basefabric contains a 50-50 blend of cotton and rayon fibers; and similarresults are obtained.

Example 6 The procedure of Example 1 is followed, except that the basefabric is composed of rayon fibers (sold by Courtaulds, Inc. under thetrade name Corval) which are modified in their manufacture by reactionwith formaldehyde donor cross-linking agents; and similar results areobtained.

Example 7 The procedure of Example 1 is followed, except that thenonwoven fabric is rearranged in accordance with the process outlined inU.S. Patent 2,862,251 prior to the cross-linking treatment; and similarresults are obtained.

Example 8 The procedure of Example 1 is followed, except that thecross-linking agent is formaldehyde applied from a 2% solution with N/100 H 50 catalyst. The bound formaldehyde content of the fabric is foundto be 0.58% by chemical analysis. The product has the desirableproperties as described in Example 1.

Example 9 The procedure of Example 2 is followed, except that the acidcatalyst used is MgCI at /2% concentration in the solution; and similarresults are obtained.

Example 10 The procedure of Example 2 is followed, except that the acidcatalyst used is NI-I SCN (ammonium thiccyanate), at /2 concentration inthe solution; and similar results are obtained.

Example 11 The procedure of Example 2 is followed, except that the 8catalyst used is lactic acid, at /2% concentration in the solution; andsimilar results are obtained.

Example 12 The procedure of Example .1 is followed, except that the basefabric is bonded with 7% water insoluble hydroxyethyl cellulose; andsimilar results are obtained.

Example 13 A dry, all-rayon nonwoven fabric, made in accordance with theprocess outlined in U.S. Patent 2,862,251, weighing 225 grains persquare yard, containing about 2% regenerated cellulose deposited in thefine-line pattern (13 lines per inch), to function as a binder, isimpregnated in a mangle with a solution containing 1% Aerotex UM, and N/sulfuric acid. Solution pickup from the bath is about 100% based on theweight of the air-dried nonwoven fabric. The fabric is cured by exposureto 350 F. for two minutes. The bound-formaldehyde content of the fabricis found by analysis to be 0.35%, occurring principally in the bindercellulose, as determined by means of chemical staining tests.

At the completion of the curing operation, the fabric is laundered eighttimes; it is essentially unchanged from the original fabric. Acomparative fabric, without crosslinking treatment, shows pilling andconsiderable tearing after only five wash cycles.

Example 14 A dry all-rayon fibrous web Weighing approximately 600 grainsper square yard is bonded with regenerated cellulose uniformlydistributed throughout the fibrous web so that the final nonwoven fabriccontains about 8% binder. This nonwoven fabric is impregnated in amangle with a solution containing 1% of essentially monomericmethylolmelamine cross-linking agent (sold by American Cyanamid Co. asAerotex UM) and N/ 100 sulphuric acid. Solution pickup from the bath isabout 200% based on the weight of the air dried nonwoven fabric. Thefabric is dried by exposure to a temperature of 350 F. for two minutes.The bound formaldehyde content of the fabric is found by analysis to be0.58% occurring principally in the binder cellulose as determined bymeans of chemical staining tests.

This fabric is used as a wrapping for cheese and similar foods. Thetreated and cured fabric withstands 20 washings Without deleteriouseffect while an analogous fabric which has not undergone thecross-linking treatment, pills and loses fibers after only threewashings.

Example 15 A dry all-rayon nonwoven fabric weighing 750 grains persquare yard, containing about 4% regenerated cellulose deposited in afine line pattern (8 lines to the inch) to function as a binder, isimpregnated and mangled with a solution containing 1% monomericmethylolmelamine cross-linking agent (sold by American Cyanamid Jo. asAerotex UM) and N/ 100 sulphuric acid. Solutron pickup from the bath isabout 200% based on the weight of the air dry nonwoven fabric. Thefabric is dried by exposure to a temperature of 350 F. for two minutes.The bound formaldehyde content of this fabric s shown by analysis to be0.75% occurring principally n the binder cellulose as determined by achemical stainmg test.

After completion of the curing operation the fabric is used as a wetwiping cloth for dishes, counters, and the like. The treated and curedfabric withstands repeated washings very readily and is reasonablyabsorbent though after continued use it tends to smear when wipingsmooth surfaces such as glass or mirrors.

In a comparative test, dry all-rayon nonwoven fabric weighing 750 grainsper square yard, containing about 4% regenerated cellulose deposited ina fine-line pattern (8 lines to the inch) to function as a binder, isimpregnated and mangled with a solution containing 2 /2 of essentiallymonomeric methylolmelamine cross-linking agent (sold by AmericanCyanamid Co. as Aerotex UM) and N/ 100 sulphuric acid. Solution pickupfrom the bath is about 200% based on the weight of the air-driednonwoven fabric. The fabric is dried by exposure to a temperature of 350F. for two minutes. The bound formaldehyde content of this fabric isfound by analysis to be 1.15% occurring prncipally in the bindercellulose as determined by a chemical staining test.

The resulting fabric is unsatisfactory as a wiping cloth as itsabsorbency is low and it smears readily when rubbed across smoothsurfaces such as glass or a mirror.

What is claimed is:

1. A bonded nonwoven fabric having textile-like softness, drape, handand superior wash-resistance comprising: a web of overlapping,intersecting cellulosic fibers and a formaldehyde cross-linkedcellulosic binder, said binder being distributed throughout said web andforming bonds between said fibers, said fabric having a formaldehydecontent of from about 0.1% to 0.8% based on the weight of the fabric andthe cellulosic fibers of said fabric being substantially unbound byformaldehyde.

2. A bonded nonwoven fabric having textile-like softness, drape, handand superior wash-resistance comprising: a web of overlapping,intersecting cellulosic fibers and a formaldehyde cross-linkedcellulosic binder, said binder being distributed throughout said web andforming bonds between said fibers, said fabric having a formaldehydecontent of from about 0.15% to 0.6% based on the weight of the fabricand the cellulosic fibers of said fabric being substantially unbound byformaldehyde.

3. A bonded nonwoven fabric having textile-like softness, drape, handand superior wash-resistance comprising: a web of overlapping,intersecting cellulosic fibers and a formaldehyde cross-linkedcellulosic binder, said binder being distributed throughout said web ina predetermined pattern of spaced binder segments in bondingrelationship with the fibers passing through said segments, saidformaldehyde cross-linking being substantially only in the cellulosicbinder and the cellulosic fibers of said fabric being substantiallyunbound by formaldehyde.

4. A bonded nonwoven fabric having textile-like softness, drape, handand superior wash-resistance comprising: a web of overlapping,intersecting cellulosic fibers and a formaldehyde cross-linkedcellulosic binder, said binder being distributed throughout said web ina predetermined patern of spaced binder segments in bonding relationshipwith the fibers passing through said segments, said fabric having aformaldehyde content of from about 0.1% to 0.8% based on the weight ofthe fabric and the cellulosic fibers of said fabric being substantiallyunbound by formaldehyde.

5. A bonded nonwoven fabric having textile-like softness, drape, handand superior wash-resistance comprising: a web of overlapping,intersecting cellulosic fibers and a formaldehyde cross-linkedcellulosic binder, said binder being distributed throughout said web ina predetermined pattern of spaced binder segments in bondingrelationship with the fibers passing through said segments, said fabrichaving a formaldehyde content of from about 0.15 to 0.6% based on theweight of the fabric and the cellulosic fibers of said fabric beingsubstantially unbound by formaldehyde.

6. A bonded nonwoven fabric having textile-like softness, drape, handand superior wash-resistance comprising: a web of overlapping,intersecting cellulosic fibers and a formaldehyde cross-linkedregenerated cellulosic binder distributed throughout said web in apredetermined pattern of spaced binder segments in bonding relationshipwith the fibers passing through said segments, said fabric having aformaldehyde content of from about 0.15% to 0.6% based on the weight ofthe fabric and the cellulosic fibers of said fabric being substantiallyunbound by formaldehyde.

r 7. A bonded nonwoven fabric having textile-like softness, drape, handand superior wash-resistance comprismg: a web of overlapping,intersecting cellulosic fibers and a formaldehyde cross-linkedcellulosic binder distributed throughout said web in a predeterminedpattern :of spaced binder segments in bonding relationship with thefibers passing through said segments, the segments covering from about12% to 35% of the lateral surface of the fabric, said fabric having aformaldehyde content of from about 0.15% to 0.6% based on the weight ofthe fabric and the cellulosic fibers of said fabric being substantiallyunbound by formaldehyde.

8. A method of forming a bonded nonwoven fabric having textile-likesoftness, drape, hand and superior wash-resistance which comprises:wetting a web of overlapping, intersecting cellulo-sic fibers,adhesively bonding the fibers throughout the web with a cellulosicbinder, impregnating the bonded web with from about 0.1% to 0.8% offormaldehyde, based on the weight of the fabric, in the presence of anacid catalyst for the reaction of cellulose and formaldehyde, and dryingthe impregnated web to formaldehyde cross-link the cellulosic binder,said catalyst being in a concentration such that the pH of the fabric isnot more than 0.5 pH units less than the pH of the web just prior toimpregnation with formaldehyde.

9. A method of forming a bonded nonwoven fabric having textile-likesoftness, drape, hand and superior wash-resistance which comprises:wetting a web of overlapping, intersecting cellulosic fibers, adhesivelybonding the fibers with a cellulosic binder in a predetermined patternof spaced binder segments, impregnating the bonded web with from. about0.1% to 0.8% of formaldehyde, based on the weight of the fabric, in thepresence of an acid catalyst for the reaction of cellulose andformaldehyde, and drying the impregnated web to formaldehyde cross-linkthe cellulosic binder, said catalyst being in a concentration such thatthe pH of the fabric is not more than 0.5 pH units less than the pH ofthe web just prior to impregnation with formaldehyde.

10. A method of forming a bonded nonwoven fabric having textile-likesoftness, drape, hand and superior wash resistance which comprises:wetting a web of overlapping, intersecting cellulosic fibers, adhesivelybonding the fibers with a cellulosic binder in a predetermined patternof spaced binder segments over the surface of the web and substantiallythroughout the thickness of the web, impregnating the bonded web withfrom about 0.1% to 0.8% of formaldehyde, based on the weight of thefabric, in the presence of an acid catalyst for the reaction ofcellulosic and formaldehyde, and drying the impregnated web toformaldehyde cross-link the cellulosic binder, said catalyst being in aconcentration such that the pH of the fabric is not more than 0.5 pHunits less than the pH of the web just prior to impregnation withformaldehyde.

11. A method of forming a bonded nonwoven fabric having textile-likesoftness, drape, hand and superior wash-resistance which comprises:wetting a web of overlapping, intersecting cellulosic fibers, adhesivelybonding the fibers through out the web with a cellulosic binder,impregnating the bonded web with from about 0.1% to 0.8% offormaldehyde, based on the weight of the fabric, in the presence ofsulfuric acid having a normality of from about N/ 200 to N/50, anddrying the impregnated web to formaldehyde cross-link the cellulosicbinder.

12. A method of forming a bonded nonwoven fabric having textile-likesoftness, drape, hand and superior wash-resistance which comprises:wetting a web of overlapping, intersecting cellulosic fibers, adhesivelybonding the fibers with a cellulosic binder in a predetermined patternof spaced binder segments, impregnating the bonded web with from about0.1% to 0.8% of formaldehyde, based on the weight of the fabric, in thepresence of sulfuric acid having a normality of from about N/ 200 to 1 11 2 N/50, and drying the impregnated Web to formaldehyde 2,698,574Dougherty et a1. Ian. 4, 1955 cross-link the cellulosic binder.2,958,608 Barnard Nov. 1, 1960 References Cited in the file of thispatent OTHER REFERENCES UNITED STATES PATENTS 5 Paist: Cellulosics(1950), Reinhold, N.Y. (P. 204

2,689,194 Russell et al. Sept. 14, 1954 r li d

1. A BONDED NONWOVEN FABRIC HAVING TEXTILE-LIKE SOFTNESS, DRAPE, HANDAND SUPERIOR WASH-RESISTANCE COMPRISING: A WEB OF OVERLAPPING,INTERSECTING CELLULOSIC FIBERS AND A FORMALDEHYDE CROSS-LINKEDCELLULOSIC BINDER, SAID BINDER BEING DISTRIBUTED THROUGHOUT SAID WEB ANDFORMING BONDS BETWEEN SAID FIBERS, SAID FABRIC HAVING A FORMALDEHYDECONTENT OF FROM ABOUT 0.1% TO 0.8% BASED ON THE WEIGHT OF THE FABRIC ANDTHE CELLULOSIC FIBERS OF SAID FABRIC BEING SUBSTANTIALLY UNBUOUND BYFORMALDEHYDE.